1. Field of the Invention
The present invention relates to an organic electroluminescent (hereunder abbreviated as EL) display panel that has a plurality of organic EL devices, which are formed on a substrate in a predetermined pattern and each have a light emitting layer constituted by a thin film made of an organic compound material exhibiting electroluminescence that is the emission of light resulting from current injection.
2. Description of the Related Art
Hitherto, there have been organic electroluminescent devices (hereunder referred to as organic EL devices) serving as display devices each using a laminated element made of an organic luminescent material.
An organic EL device is constituted by serially stacking a transparent electrode, an organic EL medium, and a metallic electrode on a transparent substrate. For example, the organic EL medium comprises a single organic light emitting layer, or comprises a three-layer medium having an organic hole transport layer, an organic light emitting layer, and an organic electron transport layer, or comprises a two-layer medium having an organic hole transport layer and an organic light emitting layer, or comprises a laminated medium obtained by inserting an electron or hole injecting layer into between proper ones of such layers.
For example, an organic EL display panel of the matrix display type is constituted by serially stacking line electrodes, which include transparent electrode layer, and organic EL media, and row electrodes including metallic electrode layers each of which intersects with a corresponding line electrode. The line electrodes are each formed like a strip, and arranged at predetermined intervals in such a way as to be parallel with one another. The row electrodes are placed in a similar manner. Thus, the display panel of the matrix display type has an image display arrangement, that is, a display panel region having light emitting pixels respectively constituted by plural organic EL devices that are formed at intersections (referred to as xe2x80x9cdotsxe2x80x9d) of plural line electrodes and plural row electrodes.
The organic EL device is of the current injection type. Thus, the luminous efficiency of the device largely depends upon reduction in the resistance of each electrode line. Therefore, when the resistance of each electrode line is high, a large voltage drop is caused by electric current flowing therethrough. Thus, inconsistencies in luminance occur on the panel. Consequently, display quality is degraded.
Thus, there is the necessity for using a low resistance material for wiring of the electrodes in the display panel region on the substrate. However, the conventional organic EL device has a drawback in that especially, the material of the transparent electrode, which serves as an anode and made of indium tin oxide (hereunder referred to as xe2x80x9cITOxe2x80x9d), has a high sheet resistance.
Thus, the resistance is reduced by using low-resistance auxiliary metallic lines for wiring between the transparent electrodes (or anodes) in the display panel region. That is, patterned anodes are stacked on the substrate. Moreover, metallic lines are stacked thereon. Thereafter, an organic material layer made of an organic compound, and cathodes are stacked thereon in sequence. Thus, the devices are formed, and moreover, each of the cathodes and the anodes is formed so as to be connected to an external terminal.
However, the reduction in the resistance of the wires, such as connecting lines, provided outside the display panel region on the substrate is not attained.
The invention is accomplished in view of the aforementioned drawback. Accordingly, an object of the invention is to provide an organic EL device, which can reduce the resistance of electrode wires and realize high display quality, by a process that is easy to perform.
To achieve the above object, according to the invention, there is provided an organic electroluminescent display panel that comprises a substrate including a display panel region having a plurality of organic electroluminescent devices each including a plurality of display electrodes and an organic material layer, which are stacked, and also comprises electrically conductive connecting lines electrically connected to the electrodes formed in a domain surrounding the display panel region on the substrate. The connecting lines are lower in resistance than electrodes formed on the display panel region.
In an embodiment of the organic electroluminescent display panel of the invention, the connecting lines are constituted by electrically conductive thick portions that are thicker in comparison with the electrodes formed on the display panel region.
In an embodiment of the organic electroluminescent display panel of the invention, the surface area of the connecting lines is larger in comparison with that of the electrodes formed on the display panel region.
In an embodiment of the organic electroluminescent display panel of the invention, the connecting lines are made of a material that is lower in resistance in comparison with the material of the electrodes formed on the display panel region.
In an embodiment of the organic electroluminescent display panel of the invention, a total thickness of the connecting lines and the thick portions is larger than the film thickness of the electrode provided on a topmost surface.
In an embodiment of the organic electroluminescent display panel of the invention, the connecting lines are made of the same material as the display electrode provided on a topmost surface. Moreover, the thickness of the connecting lines is nearly equal to the film thickness of the electrode provided on the topmost surface.
In an embodiment of the organic electroluminescent display panel of the invention, the thick portions are made of the same material as the connecting lines.